A vehicle's suspension system is responsible for drive comfort and safety of vehicle occupants as the suspension carries the vehicle-body over road disturbances, and transmits all forces between the vehicle-body and road surface. To positively influence drive comfort and safety, variable dampers and/or spring elements may be added to a vehicle's suspension system to enable adaptation to various driving conditions and considerably improve the drive comfort and safety of the vehicle compared to those having suspension systems with fixed properties.
Vehicles typically have one of two types of suspension systems: solid axle suspension and/or independent suspension. In the solid axle suspension systems, opposing wheels of the vehicle are mechanically linked with a solid connection, for example, a shaft or beam. Solid axle suspension dampers and links may connect the solid shaft to a chassis of the vehicle, which limits an ability of the vehicle's suspension to deliver flexible dynamics in response to an encountered road disturbance and/or changing terrain. Because solid axle suspension systems have limitations in respect of completely controlling vehicle dynamic assignment, for example, due to the fixed architecture limits, the transfer of road input to a vehicle-body operated at a low speed over rough road condition or at a high speed is perceived by a vehicle occupant as a harsh ride. In addition, solid axle suspension systems are often heavy, transfer forces from one vehicle wheel to another, and have difficulty with lateral control. This results in a suspension that is difficult to move and, once it is moving, often very hard to stop. Consequently, articulation, directional stability, unsprung mass vibrations, and towing performance of the vehicle may be limited. Because of this, solid axle suspension systems must balance and compromise between desired drive comfort and vehicle handling.
Independent suspension systems may individually connect each wheel to the chassis of the vehicle with a corresponding hydraulic damper and/or force actuator and link. A spring element can be added to the vehicle's suspension to reduce stress on the hydraulic damper such that oscillations of at least a portion of the vehicle that is spring suspended are damped. The vehicle's force actuator via the hydraulic damper and/or spring is capable of adding and dissipating energy independent of relative displacement or velocity across the vehicle's suspension. Because of this, selective adjustment of the damping and/or stiffness characteristics of the vehicle in response to contact between the vehicle's wheels and the road surface is enabled. In some instances, the vehicle's force actuator may use controllable elements to implement force feedback such that forces that are linear combinations of measured vehicle state variables are generated. These forces may be used to relax the constraints of the vehicle's suspension system and to enhance the vehicle's stability and articulation. In this manner, the vehicle's drive comfort and handling can be simultaneously improved.
When a vehicle is driven over road disturbances or on changing terrain, it may be desirable for a vehicle driver to assign vehicle suspension dynamics via various suspension modes (e.g., on-road, off-road, rock-crawling) that are reactive or adaptive to drive comfort and/or handling of the vehicle through switchable hardware. These dual mode suspension systems are designed to have a dual mode suspension architecture that can switch between, for example, a solid axle suspension architecture and an independent suspension architecture to overcome the drawbacks of the solid axle suspension system. For example, selective adjustment of the vehicle's suspension mode based on detected road disturbances and/or changing terrain can be enabled such that a vehicle driver can switch from a solid axle suspension mode to an active suspension mode in a similar manner as switching from, for example, four wheel drive to two wheel drive. This is often considered a vehicle's first intent to assign a vehicle's dynamics through switchable hardware. Alternatively, the dual mode suspension system may be designed to switch on or off an anti-roll bar of a vehicle such that the vehicle's off-road capabilities are enhanced without sacrificing on-road vehicle safety performance.
Due to increased levels of vehicle automation, integration of a high level of vehicle intelligence to deliver vehicle dynamics that are independent from traditional vehicle operating needs (e.g., drive comfort and/or handling as described above) to achieve non-traditional vehicle performance needs is desirable.